1. Field of the Invention
The present invention relates to a method for suppressing mold formation on building parts using hydrophobic substances, and to a composition for building parts which inhibits mold growth.
An increased tendency to condensation or excessively high atmospheric humidity in rooms may have various causes. In the kitchen and bathroom, there are extreme and brief peak loads with respect to atmospheric humidity, during which condensation of the water vapor can scarcely be avoided. Such atmospheric humidity can arise, for example, through cooking, dishwashing, bathing, showering, washing or drying laundry. Long-lasting water vapor loads can also occur in bedrooms. Up to one liter of water evaporates from a person per night. This amount of water is sufficient to increase the atmospheric humidity of an approximately 50 m2 room of customary room height at a temperature of 20° C. from a given atmospheric humidity of 60% to 100%. Particularly in the area of cold bridges and/or poor external insulation, condensation may form. This condensation in turn promotes the growth of fungi. Molds require a temperature of about 20° C. and an atmospheric humidity of more than 70% for growth.
As a result of the installation of new, well insulated windows in old buildings, the condensation no longer collects on the cold single glazing, from which it subsequently runs off, but rather the condensation is deposited on the inside of the comparatively colder outer walls of the room. Mold formation, for example on roller shutter boxes or in corners of rooms, is the result. Attack by molds in new buildings also occurs as a result of constructional deficiencies, for example if the building has cold bridges in the masonry owing to constructional deficiencies.
Mold comprises fungi which populate the wall and other materials, first superficially and subsequently also deeply. Mold spots are individual, generally round fungal colonies which have germinated from a single spore. Fungus researchers distinguish about 10 000 mold varieties, only a few of which, however, are found in living rooms. There is no wall mold. Different varieties, especially the Aspergillus and Penicillium varieties, coexist in a complex manner.
In contrast to plants, fungi have no chlorophyll and are therefore not capable of obtaining their energy from sunlight. Wood or wood components, wall paints, gypsum-based plaster, flowerpot earth and dead parts of indoor plants and food serve as an energy source for fungi in the living area. Like all living beings, fungi too require water in order to thrive. If there is a lack of water, the fungus dies but does not do so immediately and instead forms so-called permanent cells. These enable the fungus to survive emergency periods. If favorable growth conditions are present again, such as, for example, sufficient humidity, it continues to growth if the “emergency period” was not sufficiently long. The spread and multiplication of the fungi take place via spores and conidia. They are produced in an unimaginable large number and spread by floating in the air. Their diameter is between 0.002 and 0.006 mm and they are therefore invisible to the human eye. However, germination and fungal growth occur only under growth conditions favorable for the respective fungus variety. Damp walls, for example, therefore constitute an ideal living space and culture medium for fungi.
It is therefore of very great economic interest to reduce the consequences of mold attack. The first visible consequences of mold attack are the occurrence of discolorations, so-called mold spots. These are initially small and point-like and then become larger and finally grow into a fungal lawn. After a relatively long-lasting attack, the affected building materials are destroyed. Wallpapers disintegrate, wood and paper become brittle, and plaster and paint peel off.
In order to prevent a building from being attacked by molds, constructional measures are required in order to avoid cold bridges and hence condensation of atmospheric humidity, for example on the inner surfaces of outer walls. These constructional measures are supported by ventilation or air purification measures. Thus, a high air exchange rate is advisable, i.e. the total room air should be exchanged at least once per hour.
2. Description of Related Art
One of the possible constructional measures for avoiding mold attack comprises moisture-storing plaster coats which are applied to the inner surface of a room. These plaster coats release the moisture to the environment again as soon as the atmospheric humidity of the environment has decreased. This makes it possible to prevent the walls from being permanently wet and hence mold attack occurring. Such moisture-storing plaster materials are available from epasit GmbH Spezialbaustoffe under the trade name Epatherm®.
The patent DE 199 13 738 C2 describes a method for stopping mold growth on the inner surfaces of a room. Here, the surface temperature of the inner surface of a room is increased to a temperature above the dew point by heat energy supplied directly to this surface. The resulting temperature difference between the surface temperature of the inner surface of a building wall and the room air temperature is dependent on the temperature and the atmospheric humidity of the environment. A disadvantage here is the high energy consumption.
Patent application DE 101 39 574 describes self-cleaning surfaces which have antimicrobial properties. The antimicrobial property is achieved by virtue of the fact that the coating material also comprises antimicrobial polymers in addition to the structure-forming particles. These surfaces inhibit the growth of bacteria, fungi and algae. However, this method has the disadvantage that expensive antimicrobially active polymers have to be used.
The Laid-Open Applications DE 199 55 153 A1 and DE 199 57 102 A1 describe the addition of 4-hydroxybenzoic esters and/or sodium alkyl-4-hydroxybenzoates as mold-inhibiting active substances in synthetic resin emulsions or in joint mortar. 4-Hydroxybenzoic esters—so-called parabens—are considered in principle to be safe. Thus, they are approved as preservatives up to a content of 0.4% by weight (cosmetics regulation of Oct. 7, 1997, German Federal Law Gazette 1 page 2410). Owing to the low molecular weight character of the parabens, they may be leached by means of the condensation forming at a cold bridge.
A wall lining material for buildings having a mold-preventing effect is described by the laid-open application DE 37 30 820. N-(Fluorodichloromethylthio)-phthalimide and N,N-dimethyl-N′-phenyl-N′-(fluoro-dichloromethylthio) sulfamide are mentioned as a preferred composition for preventing fungal attack. These ingredients were assigned only slight toxicological potential in a study by the International Programme on Chemical Safety, IPCS, carried out in 1974, but the disadvantageous ecological aspects of the introduction of halogenated compounds into the environment had not been taken into account there. Whether building materials which contain the mold-preventing substances described in DE 37 30 820 are capable of being recycled or whether they have to be deposited in landfills is furthermore unclear.
In their PCT Application WO 01/48098, the Deutsche Amphibolin-Werke von Robert Murjahn GmbH & Co. KG describe an aqueous coating material having a dirt- and water-repellent effect, which contains synthetic sheet silicates and/or colloidal silica having primary particle sizes of in each case less than 500 nm. The colloidal particles have been rendered hydrophobic and/or oleophobic on their surfaces. The coating material may contain fungicides as a functional substance. This method can scarcely be used subsequently since a large amount of energy is required both in the preparation of the hydrogel and in the drying thereof at a relatively high temperature over several days.
The abovementioned methods for suppressing mold formation in buildings according to the prior art have the disadvantage that the cold bridges in a building have to be recognized in good time. Frequently, the potential cold bridges of a building are not recognized at an early stage in the planning, construction, restoration or renovation phase. The subsequent elimination of these cold bridges of a completed building is as a rule feasible only at considerable expense or may not be feasible at all. Until the causes of the cold bridges are eliminated by constructional measures, there is, according to the prior art, only the possibility of using fungicides or wall lining materials, such as wallpaper and wall paints, which comprise fungicides. The effect of these fungicides on humans is often not yet clear, or said fungicides have an effect on humans which is harmful to health in the long term. It is also unclear as to whether these materials can be recycled or whether they have to be deposited in landfills.